1. Field of the Invention
The present invention relates to an indexing drive having a mechanism for positioning a cam relative to roller followers mounted on a follower wheel.
2. Description of the Related Art
The indexing drives are a power transmitting device whose input shaft is driven to rotate at a given speed to thereby cause its output shaft to make intermittent rotational movements such that the output shaft stops rotating every predetermined rotational angle. One popular type of conventionally-known indexing drive is shown in FIGS. 11 and 12, where a continuous rotational movement of the input shaft is converted via a cam mechanism into intermittent rotational movements of the output shaft.
Specifically, FIGS. 11 and 12 are side sectional and front sectional views, respectively, of the conventionally-known indexing drive A1, which show the interior construction of the indexing drive A1. Within a housing A2 having a hollow box-like shape, there are contained a cam A4 fixedly mounted on a cam shaft A3 functioning as the input shaft, and a follower wheel A6 fixedly mounted on the output shaft A5. A plurality of roller followers A7 engageable with the cam A4 are provided on the follower wheel A6 at equal intervals along the outer peripheral surface of the wheel A6.
As shown in FIG. 11, holes H1 and H2 are formed in a pair of opposed side walls (i.e., front and rear walls) of the housing A2, and output-shaft-bearing holders A8 and A9 are fitted in these holes H1 and H2, respectively. The bearing holders A8 and A9 have flanges F1 and F2, respectively, which project outward of the bearing holder fitting holes H1 and H2. The output-shaft-bearing holders A8 and A9 are secured at their respective flanges F1 and F2 to the walls of the housing A2 via bolts A10.
The output shaft A5 is rotatably supported in the housing A2 via bearings A11 and A12 held in the bearing holders A8 and A9. Further, two shims S are sandwiched between the housing A2 and the flanges F1 and F2 of the bearing holders A8 and A9, in order to adjust the axial position of the output shaft A5 relative to the housing A2 and set preloads on the bearings A11 and A12.
As shown in FIG. 12, other bearing holder fitting holes H of a circular shape are formed in a pair of opposed side walls (left and right side walls) of the housing A2 extending at right angles to the front and rear walls having the above-mentioned bearing holder fitting holes H1 and H2. Eccentric bearing holders A14, each having a flange F3, are fitted in these bearing holder fitting holes H and secured to the housing A2 by means of bolts A15. Bearings A16 are held in the respective eccentric bearing holders A14, and the cam shaft A3 is rotatably supported in the housing A2 via the bearings A16 and eccentric bearing holders A14.
As shown in FIGS. 13 and 14, each of the eccentric bearing holders A14 has a surface C2 for fitting engagement with the bearing holder fitting hole H, and this fitting surface C2 and an outer peripheral surface C1 of the flange F3 lie concentrically about a central axis O of the holder A14. The flange F3 has four arcuately-curved elongate recesses h formed at equal intervals along the outer periphery thereof, and each of the bolts A15 extends through one of the recesses h.
Further, each of the eccentric bearing holders A14 has a through-hole h1 through which the cam shaft A3 of FIG. 12 extends and a bearing retaining hole h2 in which the bearing A16 is fitted, and these holes h1 and h2 are formed concentrically about and axis O' displaced from the above-mentioned central axis O by a predetermined distance e. Sealing member G is inserted in the through-hole h1 to seal between the bearing holder A14 and the cam shaft A3. In generally the same manner as for the output shaft A5, a shim S' is sandwiched between the housing A2 and the flange F3 of each of the eccentric bearing holders A14, in order to adjust the axial position of the cam shaft A3 relative to the housing A2 and set a preload on the bearing A16.
In the conventional indexing drive A1 arranged as set forth above, as the cam A4 is rotated via the cam shaft A3 at a given constant speed, each rotation of the cam A4 causes the roller followers A7, engaging with the cam A4, to be pushed by the cam A4, so that the follower wheel A6 is allowed to rotate intermittently, a predetermined angle at a time, and such intermittent rotations of the follower wheel A6 are transmitted to the output shaft A5.
The conventional indexing drive A1 constructed in the above-described manner is normally assembled in the following sequence of steps a)-f):
a) The output shaft A5 is inserted in place within the housing A2 to set preloads on the bearings A11 and A12 via the shims S. PA1 b) The output shaft A5 is temporarily removed from within the housing A2, and then the cam shaft A3 is inserted in place within the housing A2 to set preloads on the bearings A16 via the shims S'. PA1 c) The output shaft A5 is installed in the housing A2, and axial positioning of the center of the cam A4 relative to the center of the output shaft A5 is effected using the shims S'. More specifically, in this step, some special coating is applied to the cam A4, and the eccentric bearing holders A14, located on opposite sides of the cam A4, are turned in the same phase to thereby adjust the direction of displacement of the axis O' from the central axis O so that the cam A4 is brought into contact with the roller followers A7. Then, accuracy of the axial positioning of the cam A4 is determined by ascertaining, via the eyes of the human operator, a degree or condition of adherence of the coating material from the cam A4 onto the roller followers A7. PA1 d) The output shaft A5 is axially positioned using the shims S' in such a way that the moving trajectory of the roller followers A7 and the axial center of the cam A4 substantially coincide with each other. In this step, the special coating is applied to the cam A4 so that accuracy of the axial positioning of the cam A4 is determined by ascertaining, via the eyes of the human operator, a degree or condition of the abutting engagement between the cam A4 and the roller followers A7 on the basis of adherence of the coating material from the cam A4 onto the roller followers A7, similarly to step c) above. PA1 e) The eccentric bearing holders A14, located on the opposite sides of the cam A14, are further rotated in the same phase to thereby produce preloads between the cam A4 and the roller followers A7. After that, the special coating is again applied to the cam A4 so that accuracy of the axial positioning of the cam A4 is determined by ascertaining, via the eyes of the human operator, a degree or condition of the abutting engagement between the cam A4 and the roller followers A7 on the basis of adherence of the coating material from the cam A4 onto the roller followers A7. PA1 f) It is ascertained whether the moving trajectory of the roller followers 7 and the axial center of the cam A4 coincide with each other. If the moving trajectory of the roller followers 7 and the axial center of the cam A4 are determined as not substantially coinciding with each other, steps e) and f) are repeated. PA1 1) The cam is inserted in place within the housing, and preloads on the cam bearings are set. PA1 2) The cam is temporarily removed from within the housing, and then the output shaft is inserted in place within the housing to set preloads on the output-shaft bearings. PA1 3) The cam is again inserted in place within the housing, and the first reference surface of each of the cam-bearing holders is positioned at a predetermined distance from the positioning reference surface of the output shaft, using a gauge, positioning jig etc. PA1 4) Axial positioning of the cam relative to the housing is performed so that the cam is placed in an appropriate engagement with the roller followers on the output shaft. PA1 5) The respective second reference surfaces of the two cam-bearing holders are pushed, via an adjustment jig or the like, to cause the cam to move toward the output shaft in parallel relation to the output shaft. The preload between the roller followers and the cam is set while ascertaining a condition of abutting engagement between them. PA1 1) The cam is inserted in place within the housing, and preloads on the cam bearings are set. PA1 2) The cam is temporarily removed from within the housing, and then the output shaft is inserted in place within the housing to set preloads on the output-shaft bearings. PA1 3) The cam is again inserted in place within the housing, and the respective reference surfaces of the two cam-bearing holders are pushed, via an adjustment jig or the like, to cause the cam to move toward the output shaft in parallel relation to the output shaft. The preload between the roller followers and the cam is set while ascertaining a condition of abutting engagement between them.
However, according to the above-mentioned assembling and position-adjusting operations for the indexing drive, where the once-inserted output shaft has to be temporarily removed from within the housing and then built into the housing again and the relative positioning between the roller followers and the cam has to be performed, on a trial-and-error basis, by checking for uneven abutting engagement between the roller followers and the cam on the basis of adherence of the coating material, there would arise a need to repeat the positioning operations when the abutting engagement between the roller followers and the cam are found uneven, which would lower the operational efficiency. Further, because the positioning operations are performed by ascertaining a condition of the abutting engagement on the basis of the coating material adherence, the human operator has to have a sufficient skill, so that uniform assemblage accuracy is difficult to achieve.
Further, the operation of causing the cam to abut against the roller followers can not be performed appropriately while checking preloads to be applied between the cam and the roller followers, e.g., from presence/absence of play between them, because the eccentric bearing holders provided on the opposite sides of the cam has to be rotated in the same phase. Thus, as the eccentric bearing holders are turned in order to apply the preloads after the axial positioning of the output, the axial center of the cam is moved eccentrically to change the positional relationship between the output shaft and the cam and the axis of the cam tends to be inclined due to a phasic difference between the rotating positions of the left and right eccentric bearing holders, which would lower the assembling accuracy.